. >> reporter: the united states marine corps made a big show of their military mobility today. in a dramatic landing at ocean beach, the marines arrived in this l-cat which stands for landing craft air cushion a 16,000 horsepower hovercraft and all 60 tons of it floats on air. this exercise isn't just for show. the marines are training with state and local emergency agencies preparing to assist with humanitarian and disaster relief when the next big earthquake hits. mayor ed lee says the marines are vital. >> the ability to carry emergency equipment from trucks to generators and all the things that we might absolutely need in a disaster we hope we never have. >> reporter: history proves roads and bridges will go down. and also proves we will need the help. modern portable emergency rooms, shock trauma units, complete with operating rooms, can be set up in hours, something the marines train for. >> this is what you would normally see in combat to take care of casualties such as we have in afghanistan. >> reporter: a local daycare came out to watch the landing. while most folks o